It is known practice to dye keratin fibers, such as human hair, with dye compositions containing oxidation dye precursors, which are generally known as oxidation bases, such as ortho- or para-phenylenediamines, ortho- or para-aminophenols and heterocyclic compounds. These oxidation bases are colorless or weakly colored compounds, which, when combined with oxidizing products, may give rise to colored compounds by a process of oxidative condensation.
It is also known that the shades obtained with these oxidation bases may be varied by combining them with couplers or coloration modifiers, the latter being chosen, for instance, from aromatic meta-diamines, meta-aminophenols, meta-diphenols and certain heterocyclic compounds such as indole compounds.
The variety of molecules used as oxidation bases and couplers allows a rich palette of colors to be obtained.
The process of oxidation dyeing comprises applying to the keratin fibers oxidation bases or a mixture of oxidation bases and of couplers with an oxidizing agent, for example aqueous hydrogen peroxide solution, leaving the mixture to act and then rinsing the fibers. The colorations resulting therefrom are typically permanent, strong and resistant to external agents, such as to light, bad weather, washing, perspiration and/or rubbing. The compositions, which are generally applied at basic pH, allow dyeing and simultaneous lightening of the fiber to be obtained, which is reflected in practice by the possibility of obtaining a final coloration that is lighter than the original color. In addition, lightening of the fiber has the advantageous effect of generating a unified color in the case of grey hair, and, in the case of naturally pigmented hair, of bringing out the color, i.e., of making it more visible.
It is also known practice to dye keratin fibers by direct dyeing. The process conventionally used in direct dyeing comprises applying to the keratin fibers direct dyes, which are colored and coloring molecules that have affinity for the fibers, leaving the dyes to act and then rinsing the fibers.
It is known practice, for example, to use direct dyes of the nitrobenzene, anthraquinone or nitropyridine type, dyes of the azo, xanthene, acridine or azine type or triarylmethane dyes, for example.
The colorations resulting therefrom are colorations that are particularly chromatic, but which are, however, temporary or semi-permanent. Specifically, the nature of the interactions that bind the direct dyes to the keratin fiber, and their desorption from the surface and/or from the core of the fiber, are such that the dyeing power and the wash-fastness or perspiration-fastness of the colorations may still be considered insufficient. Certain direct dyes may also be light-sensitive due to the low resistance of the chromophore to photochemical attack, and may lead to fading of the coloration of the hair over time.
It is known practice to use direct dyes in combination with oxidizing agents. However, direct dyes may be sensitive to the action of oxidizing agents such as aqueous hydrogen peroxide solution, and reducing agents such as sodium bisulfite, which makes them generally difficult to use under these conditions.
There is thus a real need to find chromatic direct dyes which can dye keratin fibers just as strongly as oxidation dyes, which are just as stable as oxidation dyes to light, which are also resistant to bad weather, washing and perspiration, and/or which are also sufficiently stable in the presence of oxidizing agents and reducing agents to be able to simultaneously obtain lightening of the fiber either by using lightening direct compositions containing them, or by using oxidation dye compositions containing them. There is also a real need to find direct dyes which can dye keratin fibers to obtain a very wide range of colors, in particular very chromatic colors, without forgetting the “fundamental” shades such as blacks and browns and shades with glints.